1. Field of the Invention
The present invention relates to a mobile telecommunication system, and more particularly to an apparatus and a method for controlling a priority access and channel assignment call in a mobile telecommunication system.
2. Description of the Related Art
Generally, the priority access and channel assignment (PACA) call is a channel assignment service provided to a subscriber. PACA allows a subscriber to obtain communication priority, so that when a user requests a base station (BS) make a call to a mobile station that is presently not available because its traffic channel is receiving too much traffic then the mobile station (MS) switches to a standby mode so that it may be assigned to the traffic channel when the traffic channel is idle and available. Here, the standby mode of the MS is defined as the “PACA state”, which is described in connection with FIGS. 1 and 2.
Referring to FIG. 1 there is illustrated a schematic diagram of a conventional mobile telecommunication system. It consists of a Public Switch Telecommunications Network (PSTN) 160, a Public Land Mobile Network (PLMN) 150, a mobile switching center (MSC) 130, a home location register (HLR) 140, a base station controller (BSC) 120, a base station (BS) 110, and an MS 100. MS 100 communicates with both PSTN 160 and PLMN 150. The BSC 120 performs both wired and wireless link control and hand-off. The BS 110 provides the wireless traffic channel to MS 100, which manages wireless traffic resources. The HLR 140 registers the subscriber's location, although, not shown, the visitor location register (VLR) does the same function.
In FIG. 2, there is illustrated a flow diagram that depicts a conventional process for shifting the MS to the PACA state. MS 100 is requested by the user to send a signal in step 211. If MS 100 does not request a signal be sent, then the signal stays at MS 100. In step 213, if MS 100 requests a signal be sent, MS 100 transmits an origination message to BS 110. BS 110 sends the signal as a call service request message “CM_SERVICE,” REQ to MSC 130, in step 215. Then, if MSC 130 sends an assign request message, “ASSIGN REQ” to BS 110 to assign a traffic channel for the origination message, in step 217, the BS 110 detects an available or idle traffic channel, in step 219. If there exists an idle traffic channel, the BS 110 assigns it to the MS 100, in step 221. However, if there is no idle traffic channel, the BS 110 places the MS 100 in the PACA state. Then BS 110, sends a PACA message to the MS 100, in step 225, while it also sends a channel assign fail message, “CH_ASSIGN_FAIL” which represents failure in the attempt to assign a traffic channel to the MSC 130, in step 227.
Meanwhile, the MS 100 receives the PACA display message that states, “PACA-State” which informs the user, in step 229, that the MS 100 has been shifted to the “PACA-State.” As previously stated, the PACA state indicates that the BS 110 cannot assign an available traffic channel, with a communication priority, to the MS 100 because there is no available channel. MS 100 is placed on a standby mode for a predetermined time, for example 1 minute, to periodically re-send the origination signal, until the BS 110 detects an idle traffic channel assigned to the MS. In this case, the BS 110 determines whether the MS 100 has the communication priority or not, based on the subscriber's information of the MS 100 contained in the assign request message received from the MSC 130. Thus, if an idle traffic channel occurs in the BS 110, the MS 100 is immediately connected to it from the PACA state to establish a communication channel.
However, the aforementioned conventional method does not provide the MSC 130 a method to distinguish when the MS 100 has been assigned to a traffic channel during the PACA state from the MS 100 that has been assigned to a traffic channel through the ordinary assignment process, especially in charging the subscriber. In addition, when the MS 100 is handed off from one BS to another, the former BS unnecessarily stores the subscriber's information of the MS 100, thereby increasing consumption of the resources. Moreover, when the MS 100 re-sends the origination signal in the PACA state, the subscriber's information is additionally stored and maintained in the BS, which also increases consumption of the resources as in handoff.
Therefore, a need exists for an apparatus and method that can be utilized to distinguish the MS that has been assigned to a traffic channel during the PACA state from the MS that has been assigned a traffic channel through an ordinary assignment process. In addition, there exists a need for an apparatus and method that does not store a subscriber's information of a MS.